Adds BeginFrameControl via DevTools.

cc/surfaces/display_begin_frame_source.h

Index: cc/surfaces/display_begin_frame_source.h
diff --git a/cc/surfaces/display_begin_frame_source.h b/cc/surfaces/display_begin_frame_source.h
new file mode 100644
index 0000000000000000000000000000000000000000..055137ec74d1b5ebc520e919936e2cac3c6231e3
--- /dev/null
+++ b/cc/surfaces/display_begin_frame_source.h
@@ -0,0 +1,68 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_SURFACES_DISPLAY_BEGIN_FRAME_SOURCE_H_
+#define CC_SURFACES_DISPLAY_BEGIN_FRAME_SOURCE_H_
+
+#include <memory>
+#include <set>
+
+#include "base/macros.h"
+#include "cc/scheduler/begin_frame_source.h"
+
+namespace cc {
+
+class DisplayBeginFrameSourceClient {
+ public:
+  virtual void ObserverStatusChanged() = 0;
+  virtual void BeginFrameSourceSwapping(BeginFrameSource* new_source) = 0;
+};
+
+// Wraps a target BeginFrameSource and keeps track of observers that have
+// finished a BeginFrame. Supports swapping the target source underneath it.
+class DisplayBeginFrameSource : public BeginFrameSource,
+                                public BeginFrameObserver {
+ public:
+  explicit DisplayBeginFrameSource(
+      std::unique_ptr<BeginFrameSource> target_source);
+  ~DisplayBeginFrameSource() override;
+
+  BeginFrameSource* GetTargetSource() { return target_source_.get(); }
+  void SetClient(DisplayBeginFrameSourceClient* client) { client_ = client; }
+
+  bool AllObserversFinishedFrame();
+
+  void SwapTargetSource(std::unique_ptr<BeginFrameSource>* begin_frame_source);
+
+  // BeginFrameSource implementation.
+  void DidFinishFrame(BeginFrameObserver* obs,
+                      size_t remaining_frames) override;
+  void AddObserver(BeginFrameObserver* obs) override;
+  void RemoveObserver(BeginFrameObserver* obs) override;
+  bool IsThrottled() const override;
+
+  // BeginFrameObserver implementation.
+  void OnBeginFrame(const BeginFrameArgs& args) override;
+  const BeginFrameArgs& LastUsedBeginFrameArgs() const override;
+  void OnBeginFrameSourcePausedChanged(bool paused) override;
+
+ private:
+  void ObserverStatusChanged();
+  void MaybeFinishFrame();
+
+  std::unique_ptr<BeginFrameSource> target_source_;
+  std::set<BeginFrameObserver*> observers_;
+  std::set<BeginFrameObserver*> finished_observers_;
+  BeginFrameArgs last_begin_frame_args_;
+  bool observing_begin_frames_;
+  bool frame_active_;
+
+  DisplayBeginFrameSourceClient* client_;  // Not owned.
+
+  DISALLOW_COPY_AND_ASSIGN(DisplayBeginFrameSource);
+};
+
+}  // namespace cc
+
+#endif  // CC_SURFACES_DISPLAY_BEGIN_FRAME_SOURCE_H_